I would call this rot, it sometimes goes unnoticed until it's too late, such as like this. I would let it wait a while before trying to root it if it was freshly cut from the grafting stock.

After they were cut down from the grafting stock it was dried and allowed to callous over for a minimum of 3 weeks before being placed on any soil or vermiculite. After drying on the racks, they were allowed to continue sitting there until they began rooting. Once there were many roots, they were then planted in dry soil (about 80% pumice, 10% akadama, 5% sharp sand, 5% cactus mix that includes some organic soil). They were never watered once. The reason I believe it's not typical rot is because the flesh remains firm and green, unlike other rot I've witnessed where the entire plant becomes soft and discolored. Also, the insides of these plants have varying degrees of hollowness and it looks like it might be a bacteria, microscopic parasite, or disease slowly eating away at the flesh from the inside out. When I wash away the red slime, the remaining flesh still looks healthy and firm. The plant only collapses when enough of the inside is eaten away and unable to support the weight of the shell. Also, I've purchased more than 50 plants from this seller and only one type of cultivar (the hanazonos) are doing this. I've never seen red slime like this before, ever. Anyone else seen anything like this??